This invention relates to apparatus and methods for measuring and displaying the concentrations of toxic substances in a working environment. It relates particularly to the monitoring, measuring, displaying and recording of concentration levels of such substances to which an individual worker is exposed as he moves around from place to place during a shift or other work period.
The Occupational Safety and Health Administration (OSHA) Act of 1970 emphasizes the need for standards to protect the health and to provide for the safety of workers exposed to potential hazards in their working environment.
The National Institute for Occupational Safety and Health (NIOSH) has conducted formal research to recommend standards for occupational exposure. The OSHA standards are currently established for approximately four hundred gases in a working environment. The standards are set in conformance to one or more of the following categories of concentration for each gas.
(a) Acceptable ceiling concentration (ACC). Under this standard an employee's exposure to a material shall not exceed at any time during an eight hour shift the acceptable ceiling concentration limit given for the material. If this level is not exceeded there is no chronic toxicity associated with the employee's exposure.
(b) An eight hour time-weighted average (TWA). Under this standard an employee's exposure to any material in an eight hour shift of a forty hour work week shall not exceed the eight hour time-weighted average limit given for that material.
(c) Ceiling value (CV). Under this standard an employee's exposure to any material shall at no time the ceiling value given for that material. Above this level the exposure becomes acutely toxic, and the employee is in danger of death or serious physical disability.
Some examples of these standards are:
______________________________________ Material ACC TWA CV ______________________________________ Methyl Chloride, ppm 200 100 300 Styrene, ppm 200 100 600 Hydrogen sulfide, ppm 20 10 50 Carbon Monoxide, ppm -- 50 -- Toluene, ppm 300 200 500 ______________________________________
To implement these standards it is necessary to have some equipment for monitoring the concentration levels to which the employee is exposed.
Fixed monitoring equipment has been used to sample the air in the working environment. The samples are analyzed for the concentration of the specific material. The fixed monitoring equipment has been equipped with monitoring devices that sound an evacuation alarm when the ceiling value (CV) is exceeded.
Other types of fixed monitoring equipment have continuously recorded the concentration data on strip charts. This information can be analyzed to determine if the working environment did exceed the OSHA standards at any time during the period the data was recorded.
A major problem with fixed monitoring equipment is that the sampling which occurs at various points in the working area is not necessarily directly related to the concentration to which an individual worker has been exposed in his breathing area.
To lessen this problem sampling is sometimes done at several points in the work area. However, at best, the fixed monitors cannot be keyed to the individual worker. Air currents and differences in density of materials and gases often result in the failure of the fixed monitors to accurately monitor individual worker's exposure to the materials. The problem of possibly inaccurate readings by a fixed monitor is also increased when the worker moves around the work area or leaves the work area for periods of time during the work day. This can result in inaccurate measurements, particularly when the time-weighted average (TWA) is calculated from the fixed monitor concentration output.
Portable monitors have been developed for wear by the workers. However, these monitors were mainly directed at warning the worker to evacuate the area by sounding an alarm if the material concentration exceeded an acceptable concentration for the material.